Any issues if I declare the same event listener twice?

1

for example if I was to do

A();
B();
function A():void
{
this.addEventListener(MouseEvent.MOUSE_DOWN,MD,false,0,true);
}
function B():void
{
this.addEventListener(MouseEvent.MOUSE_DOWN,MD,false,0,true);
}

I know a removeEventListener will removes them both, so I am guessing that in reality I have only one listener taking up system resources?